Obesity is a growing problem among children. They seem to eat less healthy and live a sedentary lifestyle. Children who are overweight have troubles during sport, can get depressed and suffer more consequences. But are they really to blame? The parents of these children have the responsibly of keeping their children healthy. However some parents need a little help, preventing their children to get obese. By making them aware of the lifestyle of their children, they can support their children to be more physically active. The aim was to accomplish this, with the idea of monitoring the physical activity and use this to motivate children and the family to get even more active. The function of the Sensi will be to monitor the movement and activity of children and other family members during the day and motivate them to be more active. For this concept to be effective, the children and parents need to wear it as often as possible. Therefore the Sensi should be comfortable in use and wearable during several activities. The project focuses on the needs of children and their perception of the world: What they would want from a Motion Monitor. It included a lot of parts concerning the life of a child, like social elements, personal preferences, school and the home of children. The goal of the project was to design a product that reaches children and motivates them to get physically active and stay physically active. The design should encourage children to use it and become aware of the fun of physical activity. One condition was that the design should include the motion tracking of children for obtaining insight in the behaviour of physical activity of children. The result will contain a solution, meant to be on the national market in 5 years.